The Shop > Tools
Bandsaw accuracy?
awemawson:
Blade speed needs to be way higher for wood by a factor of ten from metal. Teeth per inch needs to be way coarser for wood than metal.
My Startrite - I think it's a 10V - has a knob to pull out to change between two speed ranges which gives the 10x ratio. It also has a gauge built in by the tension knob calibrated in blade width. It also has a spinny disk thing that gives blade tpi and feet per min for different materials.
Here is a picture of the change pulley chart that I happen to have on the PC
micktoon:
Hi Ade,
I agree with the above comments and especially the blade type and sharpness, for thicker wood I use 3tpi blade and would keep for just wood too, Also I have heard it said by a few wood turners that once you have cut round blanks so been cutting curves you never get a decent straight cut out of that blade again, they keep a separate blade for straight cuts. These are fellas that have learnt by trial and error after paying good money for timber and spoiling it so there will be truth in it.
As was mentioned too, you sort of need both horizontal and vertical saws in an ideal world too, or tell the missus that anyway.
Cheers Mick
awemawson:
Ade,
A couple of photos I've taken this morning for you - it turns out mine is an 18V10
First the tension gauge nestling between the wheels (I'd be very surprised if yours doesn't have this)
Secondly the TPI / Speed / Thickness calculator
Arbalist:
Those Startrite saws are fantastic machines although I think they're more aimed at metal working. We had a couple like them where I used to work. You should be able to resaw timber on it with the right blade though and with the machine set to the right speed. Not really my field but at a guess something like a 3/4" blade with 4-6 teeth per inch? The best place I've found to get advice on blades is Tuffsaws.
http://www.tuffsaws.co.uk
Ian is a top bloke for bandsaw blades.
sparky961:
I was recently tasked with cutting 9" round hard plastic on a medium sized horizontal bandsaw. One might think this is a very easy task since plastic doesn't offer much resistance to cutting. One would be wrong.
Initially I tried just making a cut with conservative settings. Higher blade speed (only "1" and "2" on this saw), low feed rate, coarse pitch brand new blade. The result was similar to what Ade describes (I think) with a "belly" to the cut instead of being dead straight. It's hard to imagine how a blade can cut like that but if you think of taking a piece of metal banding/strapping and pushing down on edge, it will bow out to one side or the other. Even when under extreme tension it has no choice but to do this. Even with very low feed it will tend to bow a little bit then continue to follow the cut until nearing the end of the cut when the blade tries to get back in line.
After some research and discussion with others I learned that with a 1" wide blade it's pretty unlikely to be able to cut a 9" diameter piece of soft material. The cut width is limited to more like 3" or 4" for a straight cut. With a much wider blade (say 2" or 3") the cut width is increased because of the reduced tendency to bow out to the side when pushed down.
The solution might not quite apply to the original problems described, but is still important and surprising for most to learn. What worked for me was to make multiple cuts about 1/3 of the way into the material, rotating the material for each cut. I made 6 in this case, ending up with a hexagon in the middle. The last cut was completely through. The partial cuts can be higher feed but the last one needs to be appropriately light. This got me slices with faces that were very flat.
Yes, there are some cuts that didn't quite line up but much better than the 1/4" or so dip into the material on the first few attempts.
As many have already mentioned, lots of factors affect a bandsaw's ability to cut well. I like to set up a saw so it cuts absolutely square, and can't stand a dull blade or missing sections of teeth. That way I can make cuts that leave very little stock to be removed by machining. This is efficient in terms of time and material wastage. I can honestly say that with a well set-up machine I'm familiar with I can usually cut within 0.015" of my desired dimension on the first try. A little more time spent getting things right at the saw can save a lot more time at another machine.
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